The "dawn chorus" came in on time, salvos of missiles crashing down with shattering noise, burning buildings, killing and maiming people. It was the start of another day in Misrata, the city whose fate may decide the military outcome of this brutal civil war.

The besieged and battered bastion has become Libya's Stalingrad. The fall of Misrata would not only be a huge symbolic and psychological triumph for Muammar Gaddafi, but also end significant opposition to his rule in the west of the country.

It is this defiance and determination only 150 miles from where he sits in Tripoli that seem to enrage the dictator of Libya. The daily rocket and artillery attacks are vengeful and often indiscriminate, destroying homes and killing and maiming civilians. More than 200 attacks have been launched in the past 48 hours, killing 40 people and injuring 105 others.

Even by the standards of Misrata, the bombardment at the end of the week was particularly brutal. Missiles landed in residential areas, on a school, and in a street on which a queue outside a bakery had formed. Some people waiting for bread escaped the initial onslaught and fled to a garage that promised protection. But the next round hit the entrance, starting a fire from which they could not escape. Among those to die was a mother aged 33 and her two daughters, both under 10.

The funerals took place at a children's playground that had become the makeshift cemetery of the Ghasr Ahmed district where most of the fatalities had taken place. (The official graveyard had become too dangerous because of sniper fire.) Ahmed Wahid Nesri was going there to bury his son, Amar. The 14-year-old had been running home when he was cut down by flying shrapnel. "His body had been cut so badly. I hope it ended quickly, otherwise there would have been too much pain," he said. "I could not let his mother see that. I do not know how many others will end up like this. How much longer will this go on?"

There is no respite in Col Gaddafi's attempts to bring Misrata to heel. Time after time, his troops' try to cut the city's only lifeline, its access to the sea, are repulsed in fierce street fighting. There is always the fear that, with their superior numbers, the regime's forces could eventually break through and seize the port complex. But the revolutionaries undoubtedly benefit from being in an urban terrain they know well. And, unlike the east of the country, where the inept rebel forces have fled from loyalist fire, the Misrata fighters are tough, resilient and organised.

Members of the resistance here recount a recent example of attempted help from Benghazi in the east. A group of 30 Shabaab volunteer fighters from the capital of "Free Libya" had arrived to show the locals how to carry out their campaign. They were back home within 48 hours of their first experience of insurrection, Misrata-style.

The departure took place after a visit to Tripoli Street, which has become a focal point of clashes. Part of the long thoroughfare is a snipers' alley for the regime where civilians had been shot before the area became deserted. Other stretches are a free-fire zone for both sides, with damaged buildings changing hands by the hour. Stocks still remain behind the broken frontage of some shops, including a sports store with Manchester United and Chelsea banners.

One fighter, Ashraf Ibrahimi, was at pains to stress the revolutionaries' gratitude for Nato air strikes. "But we really need more. This is not an equal contest. It is in the interest of the West that Misrata stay alive. Gaddafi says the revolution is al-Qa'ida, which is nonsense. In Misrata, we have the highest literacy rate in the country. Our arguments here are whether we have an American- or European-style system once we are a democracy."

Three separate blasts a little to the south were followed by a convoy: one of Misrata's three ambulances and two cars being used for emergency rescues was going to a home hit in a missile strike. The injured were taken to a hospital already full from previous attacks. Dr Abdul-Baset Hussein's home, where I had stayed on arriving in the city, had been badly damaged in another missile attack, forcing him to move his family. Looking at the new arrivals on stretchers, he shook his head. "We really need more of everything. We don't have anything like enough ventilators. There are patients who would recover in any hospital with decent facilities. Here we cannot save them. For a doctor and a human being, that is a terrible thing to see. You know there is a wider aspect to this. These daily attacks are deliberate; it is a test of just how much pressure a society can sustain, how many losses we can take. Gaddafi means to break us, so this squeeze will continue."

The importance the regime attaches to capturing Misrata is reflected in the extent of the damage it is prepared to inflict. Western warplanes repeatedly hit heavy guns, but replacements keep coming. Losses in manpower appear to be more difficult to replenish for Col Gaddafi's army. Those killed and captured by rebel fighters are getting younger. Seventeen-year-old Abdurahaman Abu Salem was a prisoner at a local hospital after surgery for stomach wounds. He had been shot, he claimed, by one of his own officers after refusing to take part in an advance.

The account may or may not be true, delivered as it was by a frightened young man under guard. But the terror he felt at the front line was real enough. "I thought I was in hell. There was so much firing. There were people falling, blood everywhere. I did not think I would live." His next words were whispered: "I haven't seen my family for a long time. I don't know if I will see them again. I wish all this fighting would end."